1. Advanced Programming in Java
Basic Concepts
Mehdi Einali

2. agenda Review User input Strong type checking
Scanner
Strong type checking
Other flow-control structures
switch
break & continue
Strings
Arrays

3. review Variables Operators Methods Conditions Loops
Primitive data types
Operators
Methods
Parameter passing
Call by value
Conditions
If, else, else if
Loops
while
do-while
for

4. Variables
Variables defined and initialized

5. Variables 2 types of variables There is no global variables
Class variables(Fields)
Local variables
Method Variable
Method parameter
Block Variable
There is no global variables
Java use static binding for variables
Block variable can be defined only when there not upper scope variable in method

6. Variables
A variable always refers to its nearest enclosing binding.(Scoping)

7. User Input Print on console How to read from console? Scanner Example:
System.out.println
How to read from console?
Scanner
Example:
Scanner scanner = new Scanner(System.in);
int n = scanner.nextInt();
double d = scanner.nextDouble();

8. Example
Scanner scanner = new Scanner(System.in); int a = scanner.nextInt(); int b = scanner.nextInt(); long pow = power(a,b); System.out.println(pow);

9. Type Checking Java has a strong type-checking mechanism
Some assignment is not permitted
int intVal = 2;
long longVal =12;
intVal = longVal;Syntax Error
longVal = intVal;OK
intVal = (int)longVal; OK (Type Casting)

10. Direct Type cast The arrows are transitive
All other conversions need an explicit cast
boolean is not convertible
char is a special type

11. Type Conversion Grid

12. Type Conversion N : the conversion cannot be performed
Y : the conversion is performed automatically and implicitly by Java
C : the conversion is a narrowing conversion and requires an explicit cast
Y* : the conversion is an automatic widening conversion, but that some of the least significant digits of the value may be lost by the conversion

13. Example floating-point types are approximations of numbers
i = ; //a big integer
f = i; //f stores and approximation of i
System.out.println(f);//output : E8
i = (int) f;
System.out.println(i); //output :
floating-point types are approximations of numbers
They cannot always hold as many significant digits as the integer types

14. Comparison Compare doubles
Using == with float or double is an anti-pattern
An infinite loop:
for (float f = 10f; f != 0; f -= 0.1) {
System.out.println(f); }

15. Numeric Assignments Numeric Suffix Assignment Overflow
Double d = d;
Float f = 123f;
Long l = l;
byte b = 127;//Nothing
Assignment Overflow
Large long to int
Lower bits are used
No runtime error
Large double to integer
Brings a max int

16. Operators and cast
Division (“/”) operates differently on integers and on doubles!

17. Flow controls

18. Structured programming
Sequence
Selection
If-else
switch-case
Iteration
for
while
do-while

19. Block
Sometimes a group of statements needed to be executed in all or nothing manner
It is same as single
statement and can
be replaced with a
method

20. Block Variable

21. If-else Braces is optional for single statement
Remember: place braces for clarify for indentation
else will bind to last if

22. Short cut Boolean evaluation
&& vs & , || vs |

23. Loop-1
Constructs
Initialize
Step
Termination condition

24. Watch out infinite loop

25. Switch statement switch (i) { case 1: System.out.println("1"); break;
default:
System.out.println("default"); }

26. Break
Jump out of loop block

27. Continue
Stops the execution of the body of the loop and continues from the beginning of the loop

28. Nested loop outer: for (int i = 0; i < 10; i++){
inner: for (int j = 0; j < 10; j++) {
if (j == 2){
break outer;
} else {
System.out.println(i);
System.out.println(j);
continue inner; }

29. 1 2 3 4 5 6 7 8 9
Switch without break

30. Comments Comments are ignored by compiler One-line comment
//nextInt = scanner.nextInt();
Multiple-line comment
/*nextInt = scanner.nextInt();
for(int i=0;i<nextInt;i++){
System.out.println(i);
} */
Javadoc comments
/**
* ... text ... */

31. String

32. String A sequence of characters Character: Strings:
char ch = ‘a’;
char ch = ‘1’;
char ch = ‘#’;
Strings:
String st = “Ali”;
String st = “123”;
String st = “1”;
String st = “”;
String is not a primitive type

33. String String in C and C++ Some functions String in java is a class
char* and char[]
\0 at the end of String
Some functions
strlen, strcpy, …
String in java is a class
String in java is not equal to char[]
Constant strings
“salam!”
“Hellow World!”

34. String and other types String input = "Nader and Simin, A Separation";
char ch = input.charAt(0);
int i = input.indexOf("Nader");
int j = input.lastIndexOf("Simin");
String newS = input.replace("Separation", "Reconciliation");
String sth = newS + ch + i + j;
System.out.println(sth);

35. String methods charAt concat  plus (+) operator contains startsWith
endsWith
indesxOf  first index of sth
lastIndexOf
replace
substring
length
split

36. Immutable String String in java is an immutable class
After creating a string, you can not change it
If you want to change it, you should create a new string
There is no such methods for strings:
setCharAt(int)
setValue(String)
Methods like replace and replaceAll, do not change the value
They return a new String

37. example What is the output of this code? String str = "Gholi";
str.replaceAll("li", "lam");
System.out.println(str);
String replaced =
System.out.println(replaced);

38. Data Hierarchy
Bit
Byte
Character
Word

39. Java Characters Some characters are special characters
Special characters are shown using backslash
Examples:
New line: \n
Tab : \t
Double-quote : \”
Single-quote : \’
Backslash : \\

40. Arrays

41. Array Collections of related data items
related data items of the same type
Arrays are fixed-length entities
they remain the same length once they are created
An array is a group of variables
called elements
containing values that all have the same type
The position number of the element is it’s index
Array elements are sequentially located in memory

43. samples char ch = array[n]; Create an array of 10 integer elements
int[] array = new int[10]; int array[] = new int[10];//equal
Create an array of n characters
char[] characters = new char[n];
Change value of 5’th element
array[5] = 12;
Retrieving value of n’th element
char ch = array[n];

44. Array Creation Shortcut
char[] array = new char[3];
array[0] = 'a';
array[1] = 's';
array[2] = 't';
The above code can be rewritten as:
char[] array = {'a','s','t'};
Other examples:
int[] numbers = {1,2,3,5,9,123};
boolean[] b = {true, true, false, true};

45. Multidimensional Arrays
int[][] matrix = new int[3][4];
matrix[2][3] = 2;
System.out.println(matrix[2][1]);

46. Unbalanced Multidimensional Array
int[][] matrix = new int[3][];
matrix[0] = new int[2];
matrix[1] = new int [5];
matrix[2] = new int [4];
matrix[2][3] = 2;
System.out.println(matrix[2][1]);
matrix[0][3] = 2;//Runtime Error
ArrayIndexOutOfBoundsException

47. Quiz (5min)
e)exception b

48. end